华北克拉通北缘早二叠世堆晶岩及其构造意义  

Early Permian Cumulates in Northern Margin of North China Craton and Their Tectonic Significances

作　　者：邵济安[1,2] 田伟[1,2] 张吉衡[3] 

机构地区：[1]北京大学造山带与地壳演化教育部重点实验室,北京100871 [2]北京大学地球与空间科学学院,北京100871 [3]中国科学院计算地球动力学重点实验室,中国科学院大学,北京100049

出　　处：《地球科学（中国地质大学学报）》2015年第9期1441-1457,共17页Earth Science-Journal of China University of Geosciences

基　　金：国家自然科学基金项目(No.41172196)

摘　　要：目前对华北克拉通北缘早二叠世基性－超基性岩成因有不同认识，其中，一种流行的观点是它们与“安第斯型大陆边缘”的活动有关．通过对冀东地区堆晶岩的研究对这一观点进行了讨论．华北克拉通北缘断续分布了受丰宁－隆化岩石圈断裂控制的早二叠世基性－超基性堆晶岩，堆晶岩的 SHRIMP 锆石 U-Pb 年龄为280～300 Ma．通过岩相学的研究，确认这是一套由纯橄岩、橄辉岩、辉石岩、角闪岩、辉长岩、闪长岩、斜长岩等不同岩性组成的堆晶岩，进一步可分为层状堆晶岩和环状堆晶岩，它们有着明显的堆晶结构．矿物学研究显示堆晶岩中角闪石、辉石、金云母等均具有高镁、高铬的幔源组分特征．不同组分堆晶岩的 Sr／Ba 比值不随熔融程度变化，具有分离结晶的趋势．相近的稀土配分形式和过渡族元素组成显示了它们的同源性．从本区晚古生代和早中生代堆晶岩的对比中，结果表明早二叠世这期堆晶岩具有初始裂谷岩浆的特征，它传递了华北克拉通陆壳从稳定向活动转化的最早信息．从区域角度看，这期活动有着更大范围的深部动力学背景．Understanding about genesis of the Early Permian basic-ultrabasic rocks in the northern margin of North China craton are varied,with one of the influential viewpoints suggesting that they are related with activities of “Andes-type continental mar-gin”,which is discussed in this paper based on researches of the cumulates in east Hebei Province.Early Permian basic-ultrabasic cumulates controlled by Fengning-Longhua lithospheric faults are distributed discontinuously in the northern margin of North China craton.The SHRIMP Zircon U-Pb ages from cumulates are 280-300 Ma.Petrographic studies confirm that the complexes consist of a suite of cumulates including dunite,pyroxenite,amphibolite,gabbro,diorite,anorthosite,and so on,which in turn can be further divided into layered and circular ones,both with obvious cumulate texture.Mineralogical stud-ies show that hornblende,pyroxene,and phlogolite in cumulates all are characterized by mantle sourced components of high Mg and high Cr.Sr/Ba ratio of cumulates with different components does not change with their melting degrees,showing that cumulates possess a fractional crystallization trend.Similar REE patterns and transition group elements reveal their consanguin-ity.Comparison of cumulates of the Late Paleozoic with those of the Early Mesozoic from the concerned area indicates that these Early Permian cumulates have characteristics of an initial-rift magma,which offers the earliest evidence of the transforma-tion from the stable to the active one of continental crust of North China craton.Viewed from broader regions,activities of this period in this area are driven by deeper geodynamics.

关 键 词：华北克拉通北缘 早二叠世 堆晶岩 壳幔过渡带 伸展背景 构造 

分 类 号：P581[天文地球—岩石学]